1. Field of the Invention
The present invention relates to a valve operating control system for an internal combustion engine, including a cam switching type, first valve operating characteristic changing mechanism, and a cam-phase changing type, second valve operating characteristic changing mechanism.
2. Description of the Prior Art
An internal combustion engine is known from Japanese Patent Publication No. 5-43847, which includes a cam switching type valve operating characteristic changing mechanism for stepwise controlling the valve lift and the opening angle of an intake valve or an exhaust valve for an internal combustion engine, and a cam-phase changing type, valve operating characteristic changing mechanism for continuously controlling the timing of the opening and closing of the valve.
When the cam-phase changing type, valve operating characteristic changing mechanism is mounted in an internal combustion engine including a cam switching type, valve operating characteristic changing mechanism, it is desirable that a common oil pump be used for both of the valve operating characteristic changing mechanisms and the capacity or displacement of the oil pump is suppressed to the minimum, in order to reduce the number of parts and to simplify the structure.
In general, however, the cam switching type valve operating characteristic changing mechanism is constructed to establish a high-speed valve timing by supplying hydraulic pressure from the oil pump, and to establish a low-speed valve timing by cutting-off the supplying of that hydraulic pressure. The cam-phase changing type, valve operating characteristic changing mechanism is constructed to change the cam phase by supplying hydraulic pressure selectively to the advancing chamber or the retarding chamber. If the cam phase is intended to be changed when high-speed valve timing has been established, or if the high-speed valve timing is intended to be established when the cam phase has been changed, there is a possibility that the hydraulic pressure supplied from the oil pump may be insufficient, resulting in a reduction in responsiveness and reliability of the valve operating characteristic changing control.